CVE-2026-112378: GitLab EE use of less trusted source in AI Gateway feature enablement header

The weakness is CWE-348, use of a less trusted source. GitLab's bulletin titles it "Use of Less Trusted Source issue in AI Gateway feature enablement header". It describes insufficient server-side validation in billing eligibility checks, which lets an authenticated user reach paid AI features that their subscription does not cover.

The impact is on integrity of licensing, not on data. The CVSS 3.1 vector (4.3, medium) shows network access, low privileges, no user interaction and a low integrity effect, with no confidentiality or availability effect. In practice the person at risk is the instance owner: users on an EE instance without the right add-on could consume AI features that are billed, which means cost and licence compliance problems. GitLab does not say which header or which features are involved, and it does not say the flaw allows access to other users' data.

The attacker needs a normal account on the instance. The bulletin reports no exploitation.

GitLab EE only: all versions from 17.8 before 19.3.6, 19.4 before 19.4.3, and 19.5 before 19.5.1. The GitLab CE package is not listed in the affected range for this issue even though the patch release covers both editions. Check the version in the Admin Area, on the /help page, or on the host:

dpkg -l gitlab-ee

Use rpm -q gitlab-ee on RPM-based systems.

Upgrade to GitLab 19.5.1, 19.4.3 or 19.3.6, whichever matches your release line. They were released on October 21, 2026. GitLab lists no workaround for this issue and recommends upgrading self-managed installations as soon as possible. GitLab.com already runs the fix.

The bulletin gives no log signature. Compare AI feature usage (for example Duo requests) against the users and groups that hold the matching subscription seats. Look for accounts without a seat that show AI activity in the audit events and in your billing or usage reports for the affected period.

Under certain conditions, an authenticated user could have accessed paid AI features without a valid subscription due to insufficient server-side validation in billing eligibility checks. Impacted versions: GitLab EE all versions from 17.8 before 19.3.6, 19.4 before 19.4.3, and 19.5 before 19.5.1. Fixed in GitLab CE/EE 19.5.1, 19.4.3 and 19.3.6, released October 21, 2026.